Method for combustion fuels which are ejected from an orifice in a manner to form a substantially conically shaped curtain of fuel and a device for putting the method into effect

ABSTRACT

A device and method for improving the combustion of fuels which emerge from the orifice of a burner nozzle in the form of a conically shaped fuel curtain, around which and coaxial with is a connecting envelope of combustion air. Extending coaxially with the main burner tube are further tubes which form air passages. The further tubes are provided at the ends thereof adjacent the fuel nozzle with air nozzle means which give the air a determined direction of flow relative to the radial plane, thereby creating a subpressure externally of the fuel and air cones, whereupon the cones are drawn rearwardly and outwardly with respect to the burner nozzle tip.

United States Patent 11 1 1111 3,864,073

KOlhi Feb, 4, 1975 METHOD FOR COMBUSTION FUELS [56] References Cited WHICH ARE EJECTED FROM AN ORIFICE UNITED STATES PATENTS IN A MANNER To FORM A 2.515.345 7/1950 Van Den Buschc 431/9 x SUBSTANTIALLY CONICALLY SHAPED 2,986,206 5/1961 Boelsma 431/9 X CURTAIN OF FUEL AND A DEVICE FOR 3,030,773 4/1962 Johnson i i r .1 431/9 X PUTTING THE METHOD INTO EFFECT 3,576,384 4/1971 Peczeli et alum. 239/424 3,671,171 6/1972 Dole 431/116 [75} Inventor: Martti Ilmari Kolhi, Stenhamra, y

Sweden Primary Examiner-Edward G. Favors 73 Assignee; m Consulting AB, Attorney, Agent, or Firm-Stevens, Davis, Miller &

Stockholm, Sweden Mosher pp 373,866 A device and method for improving the combustion of Relaed Application Dam fuels which emerge from the orifice of a burner nozzle [62] (S N 27 228 M h 23 P in the form of a conically shaped fuel curtain, around g' g y g g are which and coaxial with is a connecting envelope of combustion air. Extending coaxially with the main burner tube are further tubes which form air passages. [30] Foreign Application Pnomy Dam The further tubes are provided at the ends thereof ad- Mar. 24, 1970 Sweden 4010/70 jacent the fuel nozzle with air nozzle means which give the air a determined direction of flow relative to the [52] Cl 239/424 239/428 radial plane, thereby creating a subpressure externally 5 I l 431/9 of the fuel and air cones, whereupon the cones are drawn rearwardly and outwardly with respect to the burner nozzle tip.

23 Claims, 10 Drawing Figures PATENTED SHEET 10F 3 PATENTED 75 SHEET 2 [IF 3 PATENTEU FEB 4|975 SHEET 3 OF 3 METHOD FOR COMBUSTION FUELS WHICH ARE EJECTED FROM AN ORIFICE IN A MANNER TO FORM A SUBSTANTIALLY CONICALLY SHAPED CURTAIN OF FUEL AND A DEVICE FOR PUTTING THE METHOD INTO EFFECT This is a division, of application Ser. No. 127,228, filed Mar. 23, 1971 now U.S. Pat. No. 3,758,258.

The present invention relates to a method for combusting fuels which are ejected from an orifice in a manner to form a substantially conically shaped curtain of fuel which is mixed with an envelope of combustion air located substantially coaxial with the fuel curtain.

injury to the environment as a result ofimpurities discharged to atmosphere from plants fired with fossil solid or liquid fuels is becoming more and more serious. With, for example, oil fired systems used to heat dwellings, produce electrical energy etc. the waste gases normally contain, inter alia, soot, carbon monoxide, sul phur oxides and/or nitrogen oxides as a result of unsatisfactory combustion. Large systems of present day construction are normally provided with filter devices which separate, although not all, at least a major portion of the soot. On the other hand, the harmful nitrogen and sulphur dioxides pass through the filter devices and are discharged to atmosphere. In the case of housing developments in which each building is provided with a separate boiler system, it has normally not been possible for reasons of economy to equip each system with such filter devices and other contaminant separating devices. Consequently, the only possibility of solving air contamination problems in such areas is to improve the actual process of combustion, and it is therefore desirable to obtain a combustion process which is so complete that neither soot nor any other product of combustion harmful to the environment can be formed. When combustion is complete a blue flame is obtained and consequently efforts have hitherto been directed towards effecting the combustion processes in a manner whereby a yellow flame, which indicates that free carbon is present, is eliminated to the highest extent possible.

Consequently, in order to improve the combustion process in this respect and to reduce the risk of soot formation it has been necessary to experiment in practice with considerable flow velocities, both with respect to the fuel and to the air of combustion supplied to the burner. The high velocities, however, considerably impair the duration and strength of the flame, with the accompanying risk of extinguishing the same. Moreover, a troublesome high sound level is obtained. In spite of considerable efforts and steps, no burner constructions have hitherto been proposed which, particularly with respect to small systems, can be said to solve completely the problem on which the invention is based, namely that of effecting the process of combustion more economically and so completely that soot development and the formation of destructive chemical substances are eliminated. With soot-free combustion it is possible to effect the process of combustion stoichiometrically, which has a favorable effect on the formation of sulphur and nitrogen oxides. Thus, 80, is formed instead of 80;, which reduces the corrosion problems occurring as a result of the formation of sulphuric acid with the moisture contained in the waste gases.

The problems prevailing in the present connection with small and medium sized burners have been eliminated by means of the present invention, which is mainly characterized in that a condition ofsubpressure is maintained outside the curtain of fuel and the combustion air envelope located around the axis of the fuel cone, said subpressure condition holding the combustion zone displaced rearwardly and concentrating the combustion zone around the axis of the fuel cone.

The invention also relates to a device for carrying out the method and is substantially characterized in that arranged in a ring around the axis of the burner cone and externally of the fuel curtain and the combustion air envelope are members adapted to cause the atmosphere externally of the combustion air envelope and the fuel curtain to move outwardly from the cone axis to maintain a condition of subpressure which holds the combustion zone rearwardly displaced and concentrates said combustion zone around the cone axis.

The invention will now be described in more detail with reference to a number of embodiments thereof diagrammatically illustrated in the accompanying drawing, further features of the invention being disclosed in conjunction therewith.

FIG. 1 illustrates in perspective and in partially broken away view a basic condition ofa substantially coneshaped curtain of fuel issuing from the nozzle orifice of a burner and the cone of combustion air located coax ial with the fuel curtain.

FIG. 2 illustrates separately and in perspective how the outer surface of the fuel cone is influenced by a subpressure, resulting in an increased cone angle.

FIG. 3 illustrates, also in perspective, a fuel cone and a connecting cone of combustion air subjected to a subpressure on the outer surfaces thereof.

FIG. 4 shows in perspective and partly in longitudinal section an embodiment of a burner constructed in accordance with the invention and provided with means which cause the atmosphere outside the cones to move to create and maintain the necessary subpressure.

FIG. 5 illustrates how air is directed by positively guiding the same at suitable preferred and critical angles to the radial plane of the burner.

FIG. 6 illustrates the possibility of causing the positively guided air to rotate around the burner axis of a burner of the type illustrated in FIG. 4 for example.

FIG. 7 illustrates in longitudinal section a modified burner in which the desired subpressure is created by means of an ejector action.

FIG. 8 is an axial partial sectional view of a further modified burner construction with which the combustion zone is displaced rearwardly to extreme limits.

FIG. 9 illustrates a modified embodiment of the structure illustrated in FIG. 6.

FIG. 10 is an axial section of a further embodiment of the invention.

In accordance with the main principle of the invention, FIG. 1 illustrates the basic condition of a fuel spray issuing from a fuel orifice 10 of a conventional fuel nozzle II. The emerging fuel forms a conical film 12 which is atomized into fine droplets. The fuel cone 12 is surrounded by a conical envelope 13 of combustion air which emerges through a constriction 14 in a casing or the like I5 surrounding the fuel nozzle I]. In practice, the cones act upon each other and the surrounding atmosphere, but for the sake of simplicity the cones are shown in a theoretical condition and their influence on each other and the surroundings has been ignored. Although not shown in FIG. I, the fuel cone and/or the air cone are capable of rotating around their respective cone axes, either in the same direction or in opposite directions and at the same or different speeds. In practice, however, the atomized fuel is mixed with the air of combustion, and the subpressure created within the cones, as a result of the flow, tends to draw the fuel and the air of combustion together. When igniting the fuel air mixture by appropriate ignition means (not shown), a relatively long, yellow flame is obtained, which indicates that free carbon is present, because the temperature increase of the fuel air mixture is too slow. The final products obtained during the process of combustion consist of, inter alia, S S0 elemental carbon, i.e., soot and nitrogen oxides, which are deleterious to the environment, as indicated in the foregoing.

FIG. 2 illustrates the same fuel nozzle 11 as that illustrated in FIG. I, the casing 15 having been removed and the conical air envelope 13 excluded. The Figure also illustrates in chain lines the initial position of the fuel cone. The Figure illustrates diagrammatically an example of how, in accordance with the invention, the atmosphere outside the fuel cone I2 is caused to move outwardly from the burner axis in the direction of arrows 16. In this instance, it is presumed that arranged concentrically with the axis is an annular gap or ring of orifices which is or are connected to a source of subpressure, e.g., the illustrated suction fan 17 whose suction inlet opening is identified with the reference numeral l8 and the ejection outlet opening with the reference numeral 19. The air drawn into the fan is discharged through the opening 19 externally of the burner. The resulting movement of the atmosphere in the direction of arrows 16 in the zone externally of the fuel cone 12 creates a subpressure which results in the widening of the fuel cone, which thus takes the shape of a bowl 20, as illustrated in the Figure, and the cone angle of which is also considerably increased.

The helical arrow 21 indicates a flow line, which shows that in this instance the fuel bowl rotates around its axis, although it is not always necessary for the fuel bowl to rotate. Movement of the fuel bowl can be accomplished in a known manner, for example by arranging tangentially directed grooves inside the nozzle.

FIG. 3 illustrates diagrammatically how the fuel cone and the air cone are actuated in the manner described with reference to FIG. 2. FIG. 3 thus shows the nozzle orifice 10, the nozzle 11, the casing 15, the restriction 14, the initial fuel cone and air cone 12 and 13 respectively and the fuel bowl 20. Also illustrated in the Figure is a bowl-shaped envelope of combustion air 22 which is located around the fuel bowl 20 coaxially therwith. Indicated in respective bowls by helical arrows 21 and 23 are flow lines which show how the bowls may rotate. The arrows 16 shown in FIG. 2 are also shown in FIG. 3 and represent appropriate directions of movement for the atmosphere present during removal by suction of the atmosphere from the zone located substantially within the base of the arrows and which is of particular interest in connection with the invention. The Figure also illustrates how the fuel cone I2 and the combustion air cone 13 have been substantially widened. This widening of the two cones is caused by the subpressure created in the zone nearest the fuel opening as a result of air flowing out through the restriction l4 and of the subpressure which in turn is created around the cylindrical surface of the envelope of combustion air in the region radially outside the restriction 5 14. By widening the cone angles, the bowls 20 and 22 are caused to coincide, whereupon a concentrated mixture of air and fuel is obtained which when ignited gives a relatively stable combustion zone. When the subpres sure is increased, the combustion zone is moved rear- 0 wardly towards the burner nozzle and is concentrated radially inwardly. Combustion is effected more rapidly in this combustion zone than with the example described with reference to FIG. I. In this way, a more rapid increase in temperature is obtained, resulting in the suppression of soot formation and the formation of other final products harmful to the environment.

While FIGS. I-3 are intended to illustrate the principle of the method according to the invention, FIGS. 4-10 illustrate more concrete devices for putting the method of the invention into effect, further developments of the method being described with reference to these Figures.

The method according to the invention for creating a region of subpressure outside the respective fuel and combustion air cones has, in the foregoing, only been described and illustrated in principle, with reference to FIGS. I-3. The source or means for causing the atmo sphere in the zones in question to move outwardly from the common cone axis has been exemplified in the form of a suction fan or the like, which, as will be understood, only represents an extremely elementary embodiment of the method according to the invention. Furthermore, mention has been made of a method by 5 which the air flow paths are given a specific direction without the means for carrying out the method having been described in detail.

It is particularly advantageous to the method of the present invention if the combustion air and/or the fuel mist can be caused to rotate. Such rotation contributes to a more effective mixture of the fuel mist with the combustion air. One example of a burner by means of which this development ofthe method according to the invention can be carried out is illustrated in FIG. 4, in which the reference numeral 24 indicates a body surrounding the fuel nozzle 25 and widening in a direction towards the discharge end of the burner. The body 24 is extended with a tubular portion 26, which simultaneously forms a passage for the fuel and an attachment means for a number of helically arranged guide vanes 27. The body 24 and its stem 26 are encircled by two co-axial tubes, of which the inner is identified with the reference numeral 28 and the outer with the reference numeral 29. The tubes 28 and 29 are provided at their ends located around the nozzle 25 with flanges 30 and 31. Between the body 24 and its stem 26 and the inner tube 28 there is defined a flow passage 32 for air of combustion, which is given a rotary movement by the guide vanes 27, as indicated by the arrows 33. As will be seen from the Figure, the flow passage has a restriction 34, provided by the embodiment of the body 24. As a result of this restriction, the combustion air is subjected to an ejector action. Moreover, formed between the tubes 28 and 29 is a relatively narrow, angular passage through which air is forced to flow in the direction of arrows 36 out through an annular gap 37 located between the two flanges 30 and 31.

As illustrated in the Figure, the fuel issues from the nozzle opening 35 to form a bowl-shaped curtain of fuel identified in Figure 3 with the reference numeral 20. The air emerging through the restriction 34 while rotating forms a bowl-shaped envelope 22 which partially coincides with the fuel bowl 20, similar to the explanation given the reference to FIG. 3. In this instance, the combustion air bowl rotates around its axis relative to the fuel bowl 20, as shown by the arrows 33. In this way, an intensive mixture of the fuel and the air is obtained, together with a rapid combustion, as described with reference to FIG. 3. The combustion, however, can be further considerably improved by intensifying recirculation of hot smoke gases and still unburned fuel-air mixture. FIG. 4 illustrates a method of causing such recirculation by eddying the atmosphere around the zone of combustion. As will be seen from the Figure, the positively directed air emerging through the annular gap 37 in the direction of arrows 36 causes, by ejector action, the air nearest the gap 37 to rotate and form eddies 38, which lie in the form of a ring around the flange 30. In turn, the eddy movement together with the gas movement in the zone of combustion induces a very intensive eddy movement, identified by the arrow 39, whereby hot smoke gases are recirculated back to the beginning of the combustion zone. The recirculated hot smoke gases will further increase the temperature in the combustion zone, so that combustion becomes extremely intensive and is therewith also concentrated to a relatively narrow region around the burner axis, simultaneously as the combustion zone is moved closer to the burner orifice. A particularly important factor correlated with the withdrawal of the combustion zone is the flow of air through the restriction 34 around the body 24, this flow causing, by ejector action, a region of subpressure to be created in front of the body 24 around the fuel nozzle 35. It should be observed that occurring simultaneously within the two, now coinciding bowls 20 and 22 is a recirculation of hot smoke gases which is directed to wards the fuel orifice. Naturally, these hot combustion gases contribute in the aforedescribed manner to intensify the combustion in the combustion zone.

It has been discovered in connection with the invention that the angle to the radial plane for the positively directed air flow from the gap between the flanges 30 and 31 is critical or should at least be maintained within certain suitable angular regions in order for a reasonable combustion result to be obtained. In the diagrammatic view of FIG. 5 the two tubes 28 and 29 are shown with their flanges 31 and 30 directed at a negative angle of 20 to the radial plane, which is represented by the line 40. This angle of -20 is applied in the embodi ment illustrated in FIG. 4. Experiments have shown, however, that it is possible to direct the gas flow positively at an angle of between and 60 to the radial plane, as is diagrammatically illustrated in FIG. 5. Particularly suitable angular areas are those which extend at +5 to 30 to the radial plane and which extend outwardly from the nozzle axis in accordance with the invention.

It can also be to advantage at the same time to direct the gas flow positively at an angle to the radius of the aforementioned radial plane, and by way of example reference is made to the perspective, cut away view of the burner illustrated in FIG. 6. The arrows 41, which illustrate the positively directed gas flow, are thus in this instance directed at an angle to lines extending perpendicularly to the axis of the burner nozzle. Such positively directed movement can be produced, for example, by causing the air advanced between the tubes 28 and 29 to move in a helical path and to permit the air to emerge in the direction of arrows M. In accordance with another alternative, the inner edge surfaces ofthe flanges 30 and 31 in the gap 37 can be provided with vane like members or the gap can be replaced with a ring of openings 63 which have a determined direction of orientation and which positively guide the air to flow at the desired angle to the lines extending perpendicularly to the axis of the burner nozzle, as shown in FIG. 9.

FIG. 7 illustrates diagrammatically a further embodi ment ofa burner in which the flow passage for the combustion air is incorporated in an ejector means arranged to lower the pressure in the area around the burner tip externally of the fuel air bowl. In FIG. 7, the reference numeral 42 identifies the fuel nozzle proper, which is surrounded by a body 43, past the edge surface 44 of which combustion air flows in the direction of the arrows 45 through an encircling tube 46, which terminates approximately level with the edge surface 44 of the body 43. Arranged coaxially with the tube 46 is an outer tube 47, an annular flow gap being formed in which air flows in the direction of arrows 48. Positioned at the end of the tube 47 is a ring of combined support and distance means which supports an annular, outlet member, generally indicated at 49, at such a distance from the end of the tube 47 that an annular opening 50 is formed between the end ofthe tube 47 and the outlet member 49. By cooperation between the air flows in the inner tube 46 and in the gap between the tube 46 and the outer tube 47, eddies 51 are created in the region around the burner tip and externally of the fuel-air bowl, the eddies being formed as a result of a subpressure formed externally of the gap 50 by ejector action. The eddies substantially comprise recirculated smoke gas entrained from the contact zone between the eddies 51 and the cylindrical surface of the bowlshaped envelope of the combustion zone represented by the arrows 52. As shown in the Figure, a central recirculation is also obtained within the combustion zone, as illustrated by the looped arrows 53. In this way there is obtained a recirculation ofcombustion gases in a direction towards the innermost point of the fuel bowl, whereby the fuel mist is quickly heated and rapid combustion is obtained as a result thereof. The Figure also shows by way of example the two terminals X and Y of an arbitrarily selected fuel ignition means.

FIG. 8 illustrates one half of a further modified burner construction according to the invention, in which the central body 43 illustrated in FIG. 7 is shown. With the modified construction, an inner tube 54 terminates at a certain distance behind the edge surface 44 of the body 43. An outer tube 55 having an annular or ring-shaped ejector 56 surrounds the tube 54 with an intermediate annular gap 57 and terminates at a certain distance in front of the end surface of the body 43. Combustion air flows in the direction of arrow 59 between the body 43 and the inner tube 54 through a constriction 58 and past the end of the tube 54, where the air is entrained radially outwardly by the air emerging at a higher velocity from the gap 57. The two air flows together then give rise to an ejector action when passing the ejector 56, so that a recirculation eddy, in-

dicated by the arrow 60, is created similarly to the eddy S1 in FIG. 7 with the same effect.

The radially outwardly deflected flow of combustion air, flowing through the constriction 58 in the direction of arrows 59, creates a subpressure in front of the end surface of the body 53 and around its end surface 44. This region of subpressure contributes to drawing the fuel film 61 outwardly and deflects the same rearwardly, whereupon the film 61 is surprisingly and effectively atomized into an extremely fine mist which is drawn behind the edge 44 and mixed with the combustion air. Under ideal conditions, the combustion zone will then obtain a profile such as that represented by the dash line 62.

FIG. illustrates another embodiment of the invention in which is embodied a number of gaps or passages for positively directing the air fiows at different angles to the aforementioned lines extending perpendicularly to the axis of the nozzle. In the Figure, the reference numeral 64 identifies a central tube which bears at one end thereof a fuel nozzle 65. Extending coaxially with the tube 64 are two tubes 66 and 67, there being defined between the tubes air through flow passages 68 and 69. The tube 64 is provided in the vicinity of the burner nozzle 65 with guide surfaces 70 which together with guide surfaces 71 on the tube 66 give the flow of air a direction determined by the gap. The tube 66 is also provided with guide surfaces which together with guide surfaces 73 on the tube 67 direct the air flow in a direction different to the first mentioned air flow.

It will be understood that although only two gaps have been shown further gaps may be arranged and that their configuration may be so selected that the air passing therethrough may be made to flow in any desired direction relative to the radial plane.

The invention is not restricted to the illustrated and described embodiment but can be modified within the scope of the following claims.

What we claim is:

l. A device for combusting fuel with a conical fuel curtain and a conical envelope of combustion air external of the fuel cone and a subatmospheric zone external of said conical fuel curtain, said device having a combustion zone, comprising:

a fuel nozzle having a fuel orifice to provide a sub stantially conical fuel curtain; and

at least one air exit means, located around the axis of the fuel cone, for establishing said subatmospheric zone externally of said conical fuel curtain to hold said combustion zone rearwardly withdrawn toward said nozzle and concentrated around said axis of the fuel cone in which said means is an annular gap communicating with a source of subpressure.

2. A device for combusting fuel with a conical fuel curtain and a conical envelope of combustion air external of the fuel cone and a subatmospheric zone external of said conical fuel curtain, said device having a combustion zone, comprising:

a fuel nozzle having a fuel orifice to provide a substantially conical fuel curtain; and

at least one air exit means, located around the axis of the fuel cone, for establishing said subatmospheric zone externally of said conical fuel curtain to hold said combustion zone rearwardly withdrawn toward said nozzle and concentrated around said axis of the fuel cone, in which said means includes one directionally oriented annular gap communicating with a source of pressure, said one gap being at an angle to the radial plane of the axis of the fuel cone, the angle being between +l0 and 60.

3. The device of claim 2 in which said angle is approximately 20.

4. The device of claim 3 in which the first gap is positioned to direct the gas flow at an angle to the radius of said radial plane.

5. A device for combusting fuel with a conical fuel curtain and a conical envelope of combustion air external of the fuel cone and a subatmospheric zone external of said conical fuel curtain, said device having a combustion zone, comprising:

a fuel nozzle having a fuel orifice to provide a substantially conical fuel curtain; and

at least one air exit means, located around the axis of the fuel cone, for establishing said subatmospheric zone externally of said conical fuel curtain to hold said combustion zone rearwardly withdrawn to ward said nozzle and concentrated around said axis of the fuel cone, in which said means includes ring .or orifices communicating with a source of subpressure.

6. A device for combusting fuel with a conical fuel curtain and a conical envelope of combustion air external of the fuel cone and a subatmospheric zone external of said conical fuel curtain, said device having a com bustion zone, comprising:

a fuel nozzle having a fuel orifice to provide a substantially conical fuel curtain; and

at least one air exit means, located around the axis of the fuel cone, for establishing said subatmospheric zone externally of said conical fuel curtain to hold said combustion zone rearwardly withdrawn toward said nozzle and concentrated around said axis of the fuel cone, in which said means includes one directionally oriented annular gap communicating with a source of pressure, said one gap being at an angle to the radial plane of the axis ofthe fuel cone, the angle being between +5 and 30.

7. A device for combusting fuel with a conical fuel curtain and a conical envelope of combustion air external ofthe fuel cone and a subatmospheric zone external of said conical fuel curtain, said device having a combustion zone, comprising:

a fuel nozzle having a fuel orifice to provide a substantially conical fuel curtain; and

at least one air exit means, located around the axis of the fuel cone, for establishing said subatmospheric zone externally of said conical fuel curtain to hold said combustion zone rearwardly withdrawn toward said nozzle and concentrated around said axis of the fuel cone, in which said means includes a ring of orifices communicating with a source of pressure, the ring of orifices being at an angle to the radial plane of the axis of the fuel cone, the angle being between +S and 30.

8. A burner comprising a fuel nozzle means having an opening for creating a conical fuel curtain and an annular channel mens having an outlet for providing combustion air around said fuel nozzle means, said opening being at a safe radial distance from said outlet to prevent immediate mixture of fuel and air ejected from the opening and outlet, respectively, said outlet of the annular channel means being shaped to provide a conical shaped air jacket directed away from the axis of said conical fuel curtain, the cross-section of said outlet being such that the impulse of ejected combustion air at a predetermined pressure of combustion air which is supplied is greater than the impulse of ejected fuel.

9. A burner as claimed in claim 8 wherein said annular channel means includes guide surfaces which direct the combustion air away from the axis of the conical fuel curtain.

10. A burner as claimed in claim 8 further comprising annular evacuation means arranged around an axis of the fuel nozzle means. said evacuation means including a source of subpressure.

11. A burner as claimed in claim 10 wherein said source of subpressure is an evacuation fan.

12. A burner as claimed in claim 8 further comprising an external air channel arranged around said air channel means for providing combustion air, said external air channel including an outwardly directed ejection opening for air.

13. A burner as claimed in claim 12 wherein said ejection opening of said external air channel is divided into a plurality of channels.

14. A burner as claimed in claim 8 in which said annular channel means includes one directionally oriented annular gap communicating with a source of subpressure.

15. A burner as claimed in claim 14 in which said one gap is oriented to produce a substantially toroidal shaped eddy movement pattern around the axis of said conical fuel curtain.

16. The device of claim I including another annular gap communicating with a source of pressure.

17. The device of claim I in which said means comprises ejector means.

l8. The device of claim 17 in which a plurality of ejector means are placed concentrically at different rudii.

19. The device ofclaim 18 in which at least one ejector means is directed at an angle to the remaining ejec tor means.

20. The device of claim [9 in which the ejector means are positioned to provide a subpressure behind a nozzle opening where fuel emerges such that the combustion zone is held displaced so that a portion of said zone is located behind the fuel emergence open- 21. A burner as claimed in claim 8 wherein said annular channel means includes a ring of orifices commu nicating with a source of pressure.

22. A burner as claimed in claim 21 in which said ring of orifices is oriented to produce a substantially toroidal shaped eddy movement pattern around the axis of the conical fuel curtain.

23. A burner as claimed in claim 5 including another ring of orifices communicating with a source of pres- 

1. A device for combusting fuel with a conical fuel curtain and a conical envelope of combustion air external of the fuel cone and a subatmospheric zone external of said conical fuel curtain, said device having a combustion zone, comprising: a fuel nozzle having a fuel orifice to provide a substantially conical fuel curtain; and at least one air exit means, located around the axis of the fuel cone, for establishing said subatmospheric zone externally of said conical fuel curtain to hold said combustion zone rearwardly withdrawn toward said nozzle and concentrated around said axis of the fuel cone in which said means is an annular gap communicating with a source of subpressure.
 2. A device for combusting fuel with a conical fuel curtain and a conical envelope of combustion air external of the fuel cone and a subatmospheric zone external of said conical fuel curtain, said device having a combustion zone, comprising: a fuel nozzle having a fuel orifice to provide a substantially conical fuel curtain; and at least one air exit means, located around the axis of the fuel cone, for establishing said subatmospheric zone externally of said conical fuel curtain to hold said combustion zone rearwardly withdrawn toward said nozzle and concentrated around said axis of the fuel cone, in which said means includes one directionally oriented annular gap communicating with a source of pressure, said one gap being at an angle to the radial plane of the axis of the fuel cone, the angle being between +10* and -60*.
 3. The device of claim 2 in which said angle is approximately -20*.
 4. The device of claim 3 in which the first gap is positioned to direct the gas flow at an angle to the radius of said radial plane.
 5. A device for combusting fuel with a conical fuel curtain and a conical envelope of combustion air external of the fuel cone and a subatmospheric zone external of said conical fuel curtain, said device having a combustion zone, comprising: a fuel nozzle having a fuel orifice to provide a substantially conical fuel curtain; and at least one air exit means, located around the axis of the fuel cone, for establishing said subatmospheric zone externally of said conical fuel curtain to hold said combustion zone rearwardly withdrawn toward said nozzle and concentrated around said axis of the fuel cone, in which said means includes ring or orifices communicating with a source of subpressure.
 6. A device for combusting fuel with a conical fuel curtain and a conical envelope of combustion air external of the fuel cone and a subatmospheric zone external of said conical fuel curtain, said device having a combustion zone, comprising: a fuel nozzle having a fuel orifice to provide a substantially conical fuel curtain; and at least one air exit means, located around the axis of the fuel cone, for establishing said subatmospheric zone externally of said conical fuel curtain to hold said combustion zone rearwardly withdrawn toward said nozzle and concentrated around said axis of the fuel cone, in which said means includes one directionally oriented annular gap communicating with a source of pressure, said one gap being at an angle to the radial plane of the axis of the fuel cone, the angle being between +5* and -30*.
 7. A device for combusting fuel with a conical fuel curtain and a conical envelope of combustion air external of the fuel cone and a subatmospheric zone external of said conical fuel curtain, said device having a combustion zone, comprising: a fuel nozzle having a fuel orifice To provide a substantially conical fuel curtain; and at least one air exit means, located around the axis of the fuel cone, for establishing said subatmospheric zone externally of said conical fuel curtain to hold said combustion zone rearwardly withdrawn toward said nozzle and concentrated around said axis of the fuel cone, in which said means includes a ring of orifices communicating with a source of pressure, the ring of orifices being at an angle to the radial plane of the axis of the fuel cone, the angle being between +5* and -30*.
 8. A burner comprising a fuel nozzle means having an opening for creating a conical fuel curtain and an annular channel mens having an outlet for providing combustion air around said fuel nozzle means, said opening being at a safe radial distance from said outlet to prevent immediate mixture of fuel and air ejected from the opening and outlet, respectively, said outlet of the annular channel means being shaped to provide a conical shaped air jacket directed away from the axis of said conical fuel curtain, the cross-section of said outlet being such that the impulse of ejected combustion air at a predetermined pressure of combustion air which is supplied is greater than the impulse of ejected fuel.
 9. A burner as claimed in claim 8 wherein said annular channel means includes guide surfaces which direct the combustion air away from the axis of the conical fuel curtain.
 10. A burner as claimed in claim 8 further comprising annular evacuation means arranged around an axis of the fuel nozzle means, said evacuation means including a source of subpressure.
 11. A burner as claimed in claim 10 wherein said source of subpressure is an evacuation fan.
 12. A burner as claimed in claim 8 further comprising an external air channel arranged around said air channel means for providing combustion air, said external air channel including an outwardly directed ejection opening for air.
 13. A burner as claimed in claim 12 wherein said ejection opening of said external air channel is divided into a plurality of channels.
 14. A burner as claimed in claim 8 in which said annular channel means includes one directionally oriented annular gap communicating with a source of subpressure.
 15. A burner as claimed in claim 14 in which said one gap is oriented to produce a substantially toroidal shaped eddy movement pattern around the axis of said conical fuel curtain.
 16. The device of claim 1 including another annular gap communicating with a source of pressure.
 17. The device of claim 1 in which said means comprises ejector means.
 18. The device of claim 17 in which a plurality of ejector means are placed concentrically at different radii.
 19. The device of claim 18 in which at least one ejector means is directed at an angle to the remaining ejector means.
 20. The device of claim 19 in which the ejector means are positioned to provide a subpressure behind a nozzle opening where fuel emerges such that the combustion zone is held displaced so that a portion of said zone is located behind the fuel emergence opening.
 21. A burner as claimed in claim 8 wherein said annular channel means includes a ring of orifices communicating with a source of pressure.
 22. A burner as claimed in claim 21 in which said ring of orifices is oriented to produce a substantially toroidal shaped eddy movement pattern around the axis of the conical fuel curtain.
 23. A burner as claimed in claim 5 including another ring of orifices communicating with a source of pressure. 